etpu_set4 pwmmac clarification

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etpu_set4 pwmmac clarification

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jyothsna_rajan
Contributor III

Hi, In the etpu-set4 pwmmac sample application half-cycle reload option is specified. Where can I find more details of when cycle reload is typically used?

Is there an application note that demonstrates how to invoke and use the pwmmac functions?

Refer the attached etpuc_pwmmac.c, the specific section shown below:   

       //====== begin excerpt

      else if ( (m2 == 1) && (flag0 == 1) )
       {
           .....
           // set channelX half-cycle reload flag
           tmp_half_reload_flag__master_chan = 0x800000 + GetCurrentChanNum()
           ......
            goto PWMMAC_RELOAD;
       }

       //=============== end excerpt

The param 'tmp_half_reload_flag__master_chan' appears to be a flag but is manipulated using channel number.  What is rationale behind this?

Thank you for taking time to clarify.

Best, JR

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2 Replies

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johndiener
Contributor IV

Just adding a couple of notes to David's excellent info:
- tmp_half_reload_flag__master_chan is used to retain the master channel number in order to channel context switch in PWMMACReloadPhase(), and then restore proper channel context at return time. It also passes a flag indicating reload or half reload cycle into the routine.
- as mentioned, this is an alias of register B... if modifying C code that uses register aliasing it is recommended to take special care and carefully analyze and test the results of any changes.

John Diener

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davidtosenovjan
NXP TechSupport
NXP TechSupport

The function is described in the following appnote:

https://www.nxp.com/docs/en/application-note/AN2969.pdf

Mentioned feature is described in section 3.4.

 

Half cycle update has faster response, on the other hand it’ll have higher etpu load i.e. performance limits.

Regarding source code - it seems mentioned flag tmp_half_reload_flag__master_chan (it is alias for register B) has an effect on channel switching.

 

Are you going to modify or re-use eTPU source code?

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